As compact-design, high-memory capacity and low-cost hard disk drives (HDDs) with a hard-disk medium are currently widespread use, write-once type HDDs find a wide range of applications. Once data is written on the write-once type HDD, the write-once type HDD permits data to be read only. Demand for such HDDs is mounting in the field of “archive recording” applications where long-term recording of business transactions, communication logs, personal activity, and program content data, such as movies and music, is intended.
Recording media used in the archive recording in the related art mainly include a magnetic tape, which is typically low-cost, and a recording device with an optical recording medium (such as a compact disk (CD), a digital versatile disk (DVD), or a magneto-optical (MO) disk)
When an HDD is used as a write-once recording device in the same way as the optical recording device, a one-direction writing method may be used. In the one-direction write method, for example, data may be written inwardly from the outermost track as a starting track.
A medium, such as a magnetic tape medium, permits a sequential access only. When data recording starts on the magnetic recording medium, the tape is searched from the beginning of the tape to determine a start position. A rewind operation performed prior to a search operation and the search operation are not only timing consuming but also need much energy. The repetition of such operations leads to a degradation of the recording medium.
On the other hand, the optical recording medium permits a read operation to be performed in a random access only. However, in a recording method with any particular management area or the like not arranged, a write start position is searched. A write operation is also time consuming as the magnetic tape medium.
In a method with system information or the like for managing data separately recorded, a write start position is immediately obtained. However, since information writing to the recording medium is permitted only once in such a case, another mechanism needs to be implemented.
An overwrite recording method is typically preferable to write the system information or the like for managing data. In an optical write-once medium, management data once written is virtually overwritten using rewritable information and a recording backup region. For example, Japanese Laid-open Patent Publication No. 2006-85859 discloses a plurality of improvements to such a method. One of the improvements is intended to use the recording medium in a manner such that a size limit to the recording backup region to perform a virtual overwrite operation on the management data is treated to be apparently non-existent. To this end, a recording backup region is reserved in the same region as the one storing main data and only meta management data (subject to size limit) managing the recording backup region is stored on the dedicated recording backup region.
A one-direction writing method on the HDD is advantageous over a commonly used random-writing method on the HDD in that a track width limitation caused by an effective core width of a write head is eliminated and that a narrow track pitch is provided.
FIG. 22A illustrates a known random-writing method on the HDD. Since data is written on tracks in random order (for example, (1), (2), and (3) in that order in FIG. 22A) with three tracks arranged in the direction of movement of a head as shown in FIG. 22A, tracks need to be separated from each other. The track width limitation caused by the effective core width of the write head is substantial and a surface recording density of the disk cannot be increased.
FIG. 22B illustrates the one-direction writing method on the HDD. Since data is written on tracks in a fixed order (for example, (1), (2), and (3) in that order in FIG. 22B) with three tracks arranged in the direction of movement of a head as shown in FIG. 22B, writing is performed with one track partly overlapping an immediately preceding track. The track width limitation caused by the effective core width of the write head is small and a surface recording density of the disk can be increased.
Japanese Laid-open Patent Publication No. 2001-243719 discloses other one-direction writing methods.
In accordance with the disclosed technique, see FIG. 23, tracks are grouped into a plurality of zones 2301, namely 2301(#n−1), 2301(#n), 2301(#n+1), . . . . The one-direction writing method is performed on tracks in each zone. A track pitch in the same zone, namely, intra-recording-unit track pitch 2302, is narrow. A track pitch between one track in a zone next to another track in an adjacent zone, namely, inter-recording-unit track pitch) 2303, is wide. This arrangement permits random accessing by zone. Each of the 2304 indicates reproduction elements. The 2305 indicates record track pitch.
Data may be read from tracks belonging to the same zone. When a first track in that zone is recorded, a recording and reproducing signal of the first track is first recorded. When a recording and reproducing signal of a second track is recorded, a signal interference component that results from multiplying the recording and reproducing signal of the first track by a constant value (smaller than 1) is subtracted from a reproducing signal of the second track, and the resulting difference is estimated as a correct reproducing signal of the second track. The estimated value of the second track is recorded. A signal interference component of the second track resulting from multiplying the estimated reproducing signal of the second track by a constant value is subtracted from a reproducing signal of a third track, and the resulting difference is a correct reproducing signal of the third track. This arrangement overcomes the adverse effect of leak of the reproducing signal from adjacent tracks due to the narrow track pitch (inter-track crosstalk).
Since a pitch width is modifiable by zone, variations in reproducing performance due to a difference in positions of the zones on a disk (a position difference of the zones between an inner circle and an outer circle) with respect to the track pitch of each zone is controlled.
The track pitch can be narrowed in the one-direction writing method on the HDD in accordance with Japanese Laid-open Patent Publication No. 2001-243719. If power is back on in the HDD after a power interruption, the recording operation resumes starting with a track and sector subsequent to a track and sector at which power was interrupted previously so that the rule of one-direction writing is followed.
However, the above-described related art fails to state such as a technique to resume the writing operation after power interruption. If efficiency is not important, a sequential search to determine a write start position can be performed in the same way as in the previously described magnetic tape medium. The one-direction writing HDD typically having a large memory capacity takes a long sequential search process time, and the sequential search is not a viable solution.
Since the recording method of the HDD and the recording method of the optical disk work on different principles, the above-described related art disclosed in Japanese Laid-open Patent Publication No. 2006-85859.